1. Field of the Invention
The present invention relates to a video data transceiving device, and a transceiving method thereof, and more particularly, to a video data transceiving device for transceiving video data, which performs discriminative error protection according to the significance of the video data, and a method thereof.
2. Description of the Related Art
Compressed video data is sensitive to errors due to the characteristics of compression algorithms. Therefore, research has been done on methods for coping with errors likely to be generated during the transmission of video information via a communications channel.
FIG. 1 is a block diagram illustrating the structure of a conventional video data transceiving device 1. Referring to FIG. 1, the device 1 includes a transmit stage 10 and a receive stage 12. The transmit stage 10 includes a video data supply portion 100 for supplying video data, a video data encoder 102 for compressing received video data, a forward error correction (FEC) coder 104 for adding various error correction codes including redundancy information to compressed video data provision against noise generated on a communications channel, and an interleaver 106 for interleaving a bit stream generated and output from the FEC coder 104. The receive stage 12 includes a deinterleaver 120 for recovering the interleaved bit stream, an FEC decoder 122 for decoding a signal (not shown) which is encoded by the FEC coder 104 and has error correction codes added thereto, and outputting compressed video data, a video data decoder 124 for recovering the compressed video data, and a video sync 126.
In the operation of the system 1, a video data signal output from the video data supply portion 100 is input to the video data encoder 102 and compressed. Compressed video data is input to the FEC encoder 104, and various error correction codes including redundancy information are added to the compressed video data. The interleaver 106 performs an interleaving operation of rearranging a signal output from the FEC encoder 104 in a predetermined sequence to prevent generation of burst errors liable to be generated by fading under a wireless environment, and transmits the resultant signal to a communications channel. The deinterleaver 120 performs a deinterleaving operation of receiving the signal transmitted via the communications channel and rearranging it into the original sequence. The deinterleaved signal is decoded by the FEC decoder 122. The video data decoder 124 receives the decoded signal and decompresses the decoded signal, thereby reducing video data. In this way, the conventional video data transmitting and receiving device 1 copes with noise that can be added to the communications channel.
Typically, in the device 1, it is assumed that the bits of a bit stream output from the video data encoder 102 all have the same significance. However, the compressed video data has different levels of significance. When video data of high significance is damaged by an error, degradation of the quality of an image becomes relatively serious. This problem is solved by adding a large amount of redundancy information to the video data to facilitate the restoration of the damaged video data. In this case, overhead information increases, causing a problem in that the channel rate is increased.
FIG. 2 is a block diagram of a conventional video data transceiving device for fixing the above-described problem. Referring to FIG. 2, the conventional video data transceiving device 2 includes a rate compatible punctured convolution (RCPC) encoder 202 for performing RCPC.
In the operation of the device 2, first, a video data encoder 200 divides a syntax element into several grades according to the significance of the syntax element, and transmits source significance information (SSI) including the information of the grades to the RCPC encoder 202. The RCPC encoder 202 extracts puncturing rule information and transmits coding information including the above information to a viterbi decoder 208. Accordingly, the RCPC encoder 202 performs channel coding on each grade by applying an error correction coding method, and the viterbi decoder 208 decodes a channel on the basis of the puncturing rule information, thereby improving the error correction capability.
However, in the device 2, the syntax elements of compressed video data have different SSI, and variable length coding is performed according to the SSI, so that each bit stream of video data has a different length according to the significance of the video data. For a video data bit stream prior to convolution coding, its significance is frequently changed, and the coding rule corresponding to the significance is thus also frequently changed during RCPC coding. In particular, when the coding ratio is changed with respect to small sections, there is a disadvantage in that the error correction performance of the device 2 is liable to be degraded due to the characteristics of the RCPC, as compared to when a typical convolution coding method is used.
Meanwhile, a general video compression algorithm uses a variable length, coding method, uses a prediction coding technique referring to a previous frame or a previous macro block, records coding information using administrative information, and performs decoding based on the administrative information. However, when error is generated upon coding a spatially macro block, this compression algorithm is highly likely to affect the decoding of the next and successive code word. Also, when an error is generated in the coding word of a previous frame or a macro block, the compression algorithm is highly likely to affect the decoding of the next frame or macro block. Further, when an error is generated in the administrative information, the compression algorithm may affect an entire video sequence or an entire frame. Further still, in a channel coding process, the amount of data is increased by adding various error correction codes to the compressed video data.
Consequently, in a conventional video data transceiving device, it does not control an increase of data upon channel coding according to the significance of compressed video data, causing a disadvantage in that it is difficult to use a limited channel capacity effectively.
To solve the above problems, it is an objective of the present invention to provide a video data transmitting device which performs discriminative error protectional channel coding according to the significance of video data.
It is another objective of the present invention to provide a video data receiving device for receiving and restoring video data which is channel-coded by the transmitting device.
It is still another objective of the present invention to provide a video data transceiving device which performs discriminative error protectional channel coding and transmits video data by discriminative error protection of the video data according to the significance of the video data, and receiving and restoring the channel coded video data.
It is yet another objective of the present invention to provide a video data coding method performed by the transmitting device.
It is still yet another objective of the present invention to provide a video data decoding method performed by the receiving device.
Accordingly, to achieve the first objective, there is provided a video data transmitting device comprising: a compression portion for discriminating the significance of the video data, generating region information classified by regions, compressing the video data by regions according to the region information, and outputting compressed video data; and a coding portion for coding the compressed video data by regions according to a predetermined coding rule corresponding to the significance included in the region information using the RCPC coding method, and inserting a predetermined marker.
It is preferable that the compression portion comprises: a first region information supply unit for receiving the video data, dividing the video data into regions according to the significance levels of the positions of macro blocks of the video data, and generating region information indicating the significance levels. Alternatively, the first region information supply unit can divide the received video data into regions according to the significance levels of the video data discriminated by temporal frames, or according to the significance levels of the video data discriminated by temporal frames and the significance levels of the positions of macro blocks.
Preferably, the compression portion further comprises a video data compression unit which outputs information including the number of bits for each region.
It is preferable that the coding portion comprises: a first coding rule look-up table supply unit for supplying a coding rule look-up table including information associated with punctured convolution conditions depending on the significance levels by regions; and a convolution coder for performing punctured convolution coding with reference to the coding rule look-up table, inserting a predetermined marker into a region when the coding rate of the region has changed with respect to the coding rate of the previous region, and outputting a convolution-coded bit stream.
Preferably, the first coding rule look-up table supply unit supplies a coding rule look-up table set so that a small number of puncturing processes are performed on a region of high significance, and a large number of puncturing processes are performed on a region of low significance.
It is preferable that the convolution coding unit comprises: a convolution coder for performing convolution coding at a certain rate and outputting a convolution-coded bit stream; and a marker insertion and puncturing unit for receiving the convolution-coded bit stream, and inserting a predetermined marker into a region whose coding rate has been changed while performing puncture with reference to the coding rule look-up table.
Preferably, the marker includes information representing the number of bits per region, and a larger number of fixed bits are allocated to an intra frame than to an inter frame.
It is preferable that the marker is a unique bit stream with a length of (ULxc3x97N) bits formed by sequentially inputting a first k-bit bit stream, a second unique bit stream having UL bits, and a first k-bit bit stream to a rate compatible convolution coder for performing convolution coding at a certain rate N.
Preferably, the video data transmitting device further comprises an interleaver for receiving and interleaving the convolution-coded bit stream.
To achieve the second objective, there is provided a video data receiving device comprising: a decoding portion for extracting coding rate change information indicating that the coding rule has been changed by detecting a marker from channel-coded video data, and decoding the video data according to a corresponding coding rule for each region; and a decompression portion for decompressing the video data by regions with reference to region information.
Preferably, the decoding portion comprises: a marker detector for detecting a marker satisfying a predetermined uniqueness from the channel-coded video data, and supplying coding rate change information; a second coding rule look-up table supply unit for supplying a coding rule look-up table associated with the punctured convolution conditions for each region divided according to the significance of the video data, in response to the coding rate change information; and a viterbi decoder for decoding a deinterleaved signal with reference to the coding rule look-up table and the coding rate change information and outputting compressed video data.
It is preferable that the decompression portion comprises: a second region information supply unit for supplying region information divided into regions according to the significance levels of the positions of macro blocks of video data for indicating the significance levels; and a video data decompressing unit for decompressing video data by regions with reference to the region information.
Also, it is preferable that the video data receiving device further comprises a deinterleaver for deinterleaving an interleaved signal received via a communications channel.
To achieve the third objective, there is provided a video data transceiving device comprising a compression portion, a coding portion, a decoding portion, and a decompression portion. The compression portion includes a first region information supply unit for receiving video data, dividing the received video data into regions according to the significance level of the video data, and generating region information which shows the significance level, and a video data compression unit for compressing the video data by regions according to the region information and sequentially outputting compressed video data.
The coding portion includes a first coding rule look-up table supply unit for supplying a coding rule look-up table including information associated with the punctured convolution conditions, a convolution coding unit for performing punctured convolution coding with reference to the coding rule look-up table, inserting a predetermined marker into a region when the coding rate of the region has changed with respect to the coding rate of the previous region, and outputting a convolution-coded bit stream, and an interleaver for receiving and interleaving a convolution-coded bit stream.
The decoding portion includes a deinterleaver for receiving and deinterleaving a signal transmitted via the communications channel, a marker detector for detecting a marker satisfying a predetermined uniqueness from deinterleaved signals and supplying information associated with the change of a coding rate, a second coding rule look-up table supply unit for supplying a coding rule look-up table including information associated with the punctured convolution conditions in response to the coding rate change information, and a viterbi decoder for outputting compressed video data by decoding the deinterleaved signals with reference to the coding rule look-up table and the coding rate change information.
The decompression portion includes a second region information supply unit for dividing the video data into regions according to the significance levels of the video data and supplying region information indicating the significance levels, and a video data decompressing unit for restoring compressed video data by region with reference to the region information.
To achieve the fourth objective, there is provided a video data coding method including a compressing step and a coding step. In the compressing step, the significance of video data is discriminated, region information divided into regions according to the significance is generated, and the video data is compressed by regions according to the region information. In the coding step, the compressed video data is coded by regions according to the significance included in the region information using the RCPC coding, and a predetermined marker indicating that a coding rate has been changed is inserted into the coded data.
To achieve the fifth objective, there is provided a video data decoding method including a decoding step and a decompressing step. In the decoding step, a marker is detected from the channel-coded video data, coding rate change information indicating that a coding rule has been changed is extracted, and video data is decoded according to a predetermined coding rule for each region. In the decompressing step, video data is decompressed by regions with reference to region information.